This invention generally relates to a curved slide fastener, and more particularly concerns a curved slide fastener chain from which curved slide fasteners are formed and a method for producing a curved slide fastener.
Straight slide fasteners having no curved portion therein are produced by the method including the steps of:
(a) forming a pair of fastener stringers by planting a plurality of fastener element rows of a unit length on each of a pair of fastener tapes in series and spaced relation;
(b) inter-engaging a pair of fastener stringers to form a fastener chain;
(c) washing and dewatering the fastener chain;
(d) drying the fastener chain dewatered while applying tension to the fastener chain; and
(e) forming slide fasteners by cutting the fastener chain into a unit length after applying parts, such as, bottom stops and sliders to the fastener chain.
In contrast with the aforementioned straight slide fastener, a curved slide fastener, to which this invention is directed, has a curved portion therein, so that difficulties arise in producing a curved slide fastener according to the aforementioned method for producing straight slide fasteners.
As shown in FIG. 1, a curved slide fastener F comprises a pair of fastener stringers 1 and 2, a bottom stop 14, two upper stops 16, and a slider 15. Each of the fastener stringers includes a fastener tape 3 (or 4) and a fastener element row 5 (or 6) formed by planting fastener elements on the inner side edge of the fastener tape 3 (or 4). Each fastener element row 5 (or 6) has a straight inter-engagement portion 9 (or 10) and a curved inter-engagement portion 11 (or 12). The element pitches P1 and P2 in the straight inter-engagement portions 9 and 10, respectively, are identical to one another, while the element pitches P3 and P4 in the curved inter-engagement portions 11 and 12, respectively, are different to one another. In the embodiment shown in FIG. 1, the element pitch P4 is larger than the element pitch P3, so that the curved inter-engagement portions 11 and 12, when interengaged together, represent a curved line in the plane in which the line represented by the straight inter-engagement portions 9 and 10 extends.
Referring to FIG. 9, a conventional curved slide fastener chain is illustrated from which a curved slide fastener described above is produced. The conventional fastener comprises a pair of fastener stringers 1' and 2' each having a plurality of fastener element rows 5' or 6' disposed in series and spaced relation on the inner side edge of their respective fastener tapes 3' or 4'. Each fastener element row 5' and 6' includes a straight inter-engagement portion 9' or 10' and a curved inter-engagement portion 11' or 12'. The element pitches P1' and P2' in the straight portions 9'and 10', respectively, are identical to one another, while the element pitches P3' and P4' in the curved portions 11' and 12', respectively, are different to one another. In this example shown in FIG. 9, the pitch P4' is larger than the pitch P3' so that, when the element rows 5' and 6' facing one another are inter-engaged together, the curved portions 11' and 12' curve downwardly in the drawing.
As is apparent from FIG. 9 illustrating a curved slide fastener chain according to prior art, it is noted that spaces 7' and 8' between the element rows 5' and 5a' and the element rows 6' and 6a', respectively, have the same length. Further, it is also noted that each pair of element rows e.g., 5' and 6' are inter-engaged together over their entire length.
When it is intended to produce curved slide fasteners from the aforementioned conventional curved slide fastener chain by the same method for producing straight slide fasteners mentioned hereinbefore, there occurs a problem or difficulty in preservation of the curved configuration initially given to the curved inter-engagement portions because the curved inter-engagement portions are extended by means of heat and tension applied to the curved slide fastener chain during the drying step.
In order to avoid the aforementioned problem arising in producing curved slide fasteners from the conventional curved slide fastener chain by the method for producing straight slide fasteners, as shown in FIGS. 10(A) to 10(F), curved slide fasteners are conventionally produced by the method including the steps of:
(a) forming a pair of fastener stringers 1'--1', each of which will form one of a pair of fastener stringers 1' and 2' constituting a curved slide fastener chain, by planting fastener elements on a pair of fastener tapes 3'--3' by means of a duplex planting machine 18' (refer to FIG. 10(A));
(b) forming a pair of fastener stringers 2'--2', each of which will form the other of a pair of fastener stringers 1' and 2', by planting fastener elements on a pair of fastener tapes 4'--4' by means of the planting machine 18' which is conditioned to give an element pitch different from that in the curved inter-engagement portion of the fastener stringer 1' to the curved inter-engagement portion of the fastener stringer 2' (refer to FIG. 10(D));
(c) inter-engaging each pair of fastener stringers 1'--1' 20 and 2'--2' (refer to FIGS. 10(B) and 10(E));
(d) washing, dewatering and drying the inter-engaged fastener stringers 1'--1' and 2' and 2';
(e) dis-inter-engaging each of the pairs of inter-engaged fastener stringers 1'--1' and 2'--2' (refer to FIGS. 10(C) and 10(F));
(f) inter-engaging one of a pair of the fastener stringers 1'--1' and one of a pair of fastener stringers 2'--2' together to form a curved slide fastener chain; and
(g) forming curved slide fasteners by cutting the fastener chain into a predetermined length after applying the necessary parts thereto.
However, it is very time-consuming to produce curved slide fasteners according to the method described above, because each one of a pair of fastener stringers 1' and 2' constituting a curved slide fastener chain are processed and controlled individually or separately in most of the steps explained above. Further, notwithstanding that it is desirable to wash, dewater and dry the fastener chain consisting of a pair of fastener stringers 1' and 2' inter-engaged together in order to obtain a curved slide fastener which can be smoothly opened and closed, in the method described above, the fastener stringers 1' and 2' are inter-engaged together to form a curved slide fastener chain after the washing, dewatering and drying step. Therefore, curved slide fasteners produced by the conventional method above tend to show insufficient opening and closing properties.
Furthermore, since curved slide fastener chains are usually stored in a cylindrical vessel or reeled around a reel so as to facilitate transportation thereof, the curved inter-engagement portion thereof tends to be extended by tensile force continuously applied to the fastener chains.